"Sibling Rivalry" is the twenty-second episode of season four of Family Guy, and is a sequel to the season three episode "Emission Impossible." The episode first broadcast on March 26, 2006, and was written by Cherry Chevapravatdumrong and directed by Dan Povenmire. The plot follows Stewie battling with his half-brother, Bertram, who is born to two lesbians after Peter donates sperm. Meanwhile, Lois begins excessive eating after Peter undergoes a vasectomy and loses his interest in sex.
After the vasectomy, Peter's loses his sex drive, much to the frustration of Lois, who begins excessive eating as a resolution. Peter begins to ridicule Lois due to her weight, but stops shortly after the pair have sex and discover they prefer "fat sex", opposed to their regular sex. Peter attempts to make Lois fatter to feed his urges, but Lois suffers a heart attack during sex, and the doctors remove all of the fat from her body, and she returns to her normal weight.
Shortly after birth, Bertram declares a war with Stewie for control over the playground. The pair confront each other in the playground with airplanes and helicopters, firing numerous bullets at each other. After the air battle ends with no winners, Bertram resorts to biological warfare, and infects Stewie with chickenpox. After recovering, Stewie confronts Bertram, and the pair engage in a sword fight in the play area. Stewie eventually wins, disarming Bertram, who, according to Stewie later in the episode, admitted defeat and ran away.
There was discussion among the producers of the series regarding whether Bertram should be included in the storyline, as he had not appeared in any episodes for several years. An un-used scene was intended for broadcasting which showed Stewie, while reading Where's Waldo?, saying to Brian "Oh, turn to the next page - I bet they put him in someone's utility pocket," but it was never used as it wasn't deemed funny enough for the episode. Originally, Peter singing "Milkshake" to inmates at a prison was going to be naked and push his nipples from underneath, but broadcasting standards objected; as a result, the show broadcasting Peter wearing underpants and pushing his nipples from the side. When Peter and Lois are in the restaurant and Peter leaves to 'warn the chef of Lois' arrival,' Lois was intended to say "If he won't put something in me, I will," but the gag was never broadcast.
The unsafe homeless man with whom Peter was seen leaving a youth-baseball team in Stewie's flashback was originally based on John Wayne Gacy, but people claimed he didn't look scary enough, so Povenmire changed the character completely to that of a homeless-man. The idea of Stewie and Bertram laughing as they go down the slide during their sword fight was pitched by Povenmire's wife, and, although negative about the idea at first, Povenmire included it in the episode due to the original sketch not going so well. During Peter and Lois' 'fat sex,' Peter repeatedly states "almost done, almost done;" originally, there was going to be approximately twice as many of these, but they were never included in the episode. The DVD-version of the episode shows Peter arriving at the Sperm bank, and saying to the receptionist "I have an appointment to banish a White Russian from my Kremlin," to which she replies with "This is a sperm bank, you don't have to use innuendo," and Peter concludes the conversation with "Where do I splooge?"